AQI is a composite measurement of the concentration of particulate matter below 10 and 2.5 microns, carbon monoxide, sulphur and nitrogen dioxide and ground ozone. AQI level between 0-50 is ‘Good’, 51-100 is ‘Moderate’, 101-150 is ‘Unhealthy for Sensitive Groups’, 151-200 is ‘Unhealthy’, 201-300 is ‘Very Unhealthy’, and anything above 301 is regarded as ‘Hazardous’. Kathmandu’s AQI has remained at the Maroon ‘Hazardous’ level for two days in a row.
The US Environment Protection Agency (EPA) has also colour coded various AQI levels at Green, Yellow, Orange, Red, Purple, and Maroon. The World Health Organisation (WHO)’s guidelines state that AQI should be below 35, and the concentration of particles below 2.5 microns should be below 25 μg/m³over a 24 hour period. This means Kathmandu’s pollution has been 15 times higher than the WHO standard.